Electrical component having a serrated core construction and method of making the component



y 1962 H c N. HECKEL E 3,035,115

HAVING A SERRAT ELECTRICAL PONENT' CORE CONSTRUCTION METHOD OF MAKINGTHE COMPONEN Filed Aug. 28, 1958 INVEQETOR.

HERMANN C. N. HEC L BERT T. JEFFERSON JR. 0'

1 ATTORNEYS United States Patent ELECTRICAL COMPONENT HAVDIG A SERRATEDCORE CONSTRUCTION AND METHOD OF MAK- ING THE COMPONENT Hermann C. N.Heckel, Oxford, and Robert T. Jefferson, Jr., Dayton, Ohio, assignors,by mesne assignments, to Rea Magnet Wire Company, Inc., Fort Wayne,Ind., a corporation of Delaware Filed Aug. 28, 1958, Ser. No. 757,791 2Claims. (Cl. 174-110) This invention relates to insulated electricalconductors for high temperature applications, for example, as coilswhich will withstand temperatures of 500 C. and above.

It has been found that it is desirable to provide for the free expansionand contraction of the conductor wire in electrical components which aredesigned for high temperature operation; this invention has as aparticular object the provision of a wire which is notched about itsperiphery to provide for take-up of stresses in the insulated conductorwhen the conductor is subjected to considerable temperature change.

The notched wire employed in combination with the insulation is ineffect serrated to form depressions in the wire, which depressionssuitably extend longitudinally with the wire. Preferably the wire in itsformation is drawn through a conveniently shaped die to yield thedesired wire cross-section. Such section may have the shape of a gear,star or a generally cruciform configuration.

The insulation material which is provided is inorganic and suitably intwo layers. The first layer is preferably of high softening pointmaterial and substantially inert chemically to reaction with theconductor at the temperatures of manufacture and operation. This innerlayer is covered with a layer of lower softening point material which isusually sintered to the outer layer in electric component manufacture.

The inner insulation material and the conductor are relatively slidableto permit of free elongation, and of volumetric expansion, of the wirein all directions without the exertion of substantial stress on theinsulation. This feature is emphasized by the provision of the serratedconductor since the frictional contact with the insulation is minimized.

Further, in a component such as a coil the serrations, as the conductorof the coil shrinks diametrically with temperature drop, providecavities into which the insulation may extend without undue stress. Thisfactor assists the cushioning effect provided by the insulation itself.

It is accordingly a primary object of this invention to provide a novelcombination of electrical conductor and insulation material.

It is a particular object of the invention to provide novel methods ofproducing electrical conductors and electrical components.

The invention will be more fully understood by reference to thefollowing detailed description and accompanying drawings wherein:

FIGURE 1 is a perspective View, with parts broken away, illustrating anencapsulated coil produced in accordance with the invention;

FIGURE 2 is a sectional view taken substantially on line 2--2--2 ofFIGURE 1;

FIGURE 3 is a sectional view of the insulated electrical conductorutilized in the formation of the coil of FIGURES 1 and 2; and

FIGURE 4 is a perspective view of the conductor of FIGURE 3.

Referring to the drawings, the numeral 1 generally designates anencapsulated electrical coil, the body of which is designated at 2, andthe coil is provided with encapsulating material 4. The coil is formedon a ceramic core 5. The ceramic core itself is provided with a layer oftape 6, suitably of a high softening point material, such as aluminumsilicate. Such material is sold under the trade name of Fiberfrax. Tape6 extends, as shown at 7, from one end of the coil to provide a handgrip for withdrawing the tape and the core 5 from the coil, should thesame be desired. The conductors which form the coil are indicatedgenerally at 8 in FIG URES 2 and 3.

As will be noted the copper conductor 9 is centrally disposed and is ofa substantially cruciform shape, expansion cavities 10 being definedbetween the lobes of the conductor.

Surrounding the conductor 9 and in contact therewith is a body of fibers11 which are suitably applied to the conductor in the form of continuousfilaments of a high silica content material, such as silica fiber, micaor aluminum silicate. These fibers are substantially inert chemically toreaction with the cooper and are so provided on the copper conductorthat the conductor may expand and contract longitudinally within thelayer formed by the fibers, without exerting material stress on thefibers.

Surrounding the layer 11 of silica fibers is an outer layer 12 of lowersoftening point fibers, also preferably wound on the structure in theform of continuous filaments. Suitably this material comprises acommercial E glass, for example, and preferably an E glass treated withmethacrylato chromic chloride. A suitable composition for such glass isThe sintering point of the above noted glass is about 825 C.

As may be noted most clearly from FIGURE 4 the serrations which form theexpansion cavities 10 extend longitudinally of the conductor and providefor the expansion and contraction of the conductor in such manner thatmaterial stress is not exerted on the surrounding insulation.

To form the coil of FIGURE 2 with a conductor such as that shown inFIGURES 3 and 4, the coil is wound in the normal manner on the tapecovered ceramic core. The coil is then fired at a temperature of about825 C. to effect sintering of the glass of the fibers of the outersheath. This sintering causes the glass of the fibers 12 to form asubstantially continuous film around the coil. However, there is nomaterial penetration of the fibers of silica indicated at 11 by thematerial of the outer layer since there is no true flow of thismaterial. Actually there is no stiffening of the silica fibers by theentry of glass. Therefore, the fibrous material 11 retains a materialdegree of resiliency, and this, in combination with the provision of theexpansion cavities 10, and the ability of the conductor to movelongitudinally relative to the insulation material provides for theattainment of a crackfree structure in the finished coil.

The coil, as already noted, when heated to 825 0., results in asintering of the material of the outer sheath. The time of exposure tothis temperature is approximately 30 minutes. Thereafter the coil iscooled slowly to a temperature of about 650 C. As the temperaturedecreases to about 800 C. the glass of the outer sheath hardens andthereafter the conductor contracts much more than the glass, thecontracting of the glass, in fact, being substantially insignificant.

As the conductor contracts the diameter of the coil decreases and tendsto exert stress upon the surrounding insulation. However, the fibers 11exert a cushioning eifect, inhibiting cracking of the glass of the outerlayer.

Suitably the coil is maintained about a half hour at 650 C. and then iscooled slowly to 550 C. over a period of about an hour. To relievestrains which may have been set up in the glass the coil is held at 550C. for about an hour and then cooled slowly to room temperature over aperiod of about two hours.

In this cooling there is substantially no significant contracting of theglass, either of the fibers in the layer 11 or of the coating or filmformed by the sintered glass of the outer layer. The copper may alsoshrink freely in any direction without occasioning strains in the glass,because the conductor is not bonded to the glass. Further, the provisionof a plurality of serrations uniformly disposed as in quadrature inFIGURE 3 aids the uniform contraction. In this connection it is to benoted that the sintered glass of the outer layer is milky white incontrast to glass which has been fully melted and appears quite clear.The product of the operation thus described has visible turns of thecoil which are adhered together but not mechanically well bonded by thefilm. However, the coil is sufiiciently rigid for service conditions.

To completely encapsulate the coil the material 4 is provided in theform of a. yarn and wound on the coil. The coil is then again heated toa temperature of about 875 C. to cause complete flow of the material 4,such that it takes the form illustrated in FIGURES 1 and 2. Thismaterial enters between the turns of the winding of the coil, extendsover the turns, fully encapsulating the product, but it does not extendmaterially into the interstices of the fibers 11, and therefore does notpenetrate to the conductor. Accordingly the fibers 11 remain somewhatresilient. V i p In the operation of the coil at temperatures of say 500C., for example, conductor 9 may expand freely due to the serrations,and upon contraction when cooling the layer of fibers 11 provides acushioning effect particularly between adjacent layers of the coilitself, inhibiting cracking, which normally occurs in the outer layer ofinsulation. Further the layer 11 also serves as a cushion when the coilis being heated and avoids any undue stress on the sintered glasscontinuous deposit.

The quantity of fibrous inorganic insulation material employed should besuch that oxidation of the conductor does not occur and flexibility ofthe insulated conductor is not impaired. As a guide 1.2 grams per footof the material of layer 11 and 1.5 grams per foot of the material ofthe layer 12 is satisfactory on a wire of a size of No. 18.

While the invention has been particularly described in connection with acruciform shape, it will be apparent that other shapes, such as a starshape or a gear shape, could be employed. It is only necessary that theconductor be notched in such manner to provide for the expansion of theconductor freely in all directions.

' It will be understood that this invention is susceptible tomodification in order to adapt it to different usages and conditions andaccordingly, it is desired to comprehend such modifications within thisinvention as may fall Within the scope of the appended claims.

What is claimed is:

1. An article of manufacture comprising layers of electrical insulationmaterial and an electrical conductor covered by but slippable relativeto the insulation material, said conductor being notched longitudinallyproviding serrations in the conductor, an inner layer of said insulationmaterial around said conductor being of a resilient fibrous materialwhich is substantially inert with the conductor chemically, and an outerlayer of siliceous fibers of a lower softening point than the materialof the inner layer and the conductor and which outer layer may besintered to provide a film of siliceous material over the inner layerand adhered to the inner layer, both said layers of insulation materialbeing highly flexible whereby a coil can be Wound from the insulatedconductor and then heated to sinter said outer layer to form a fullyinsulated rigid coil wherein the outer layers of insulation material ofadjacent turns of the Wire are fused together but wherein the conductoris still slippable within said inner layer of insulation material andcushioned thereby.

2. An electric coil comprising turns of an electrical conductor insuperposed relation, said conductor having longitudinally extendingserrations therein spaced about the periphery of the conductor and atleast two layers of inorganic insulation over the length of theconductor insulating the turns of the conductor and slippable upon theconductor to provide for volumetric expansion and contraction of theconductor, said insulation including an inner fibrous layer separatingthe conductor from an outer layer and being flexible and to cushion theouter layer and conductor in expansion and contraction changes of theconductor, and said outer layer also being fibrous and being flexiblewhen applied over said inner layer and also being of a lower softeningpoint than the inner layer and sinterable on said inner layer to adhereto the said inner layer without substantial penetration of the innerlayer whereby upon sintering of the outer layer after the coil is formeda cross section of the coil will reveal a rigid unitary matrixconsisting of the isntered outer layers in fused together relation andconductors distributed therein each surrounded by unsintered resilientfibrous insulation material and each conductor slippable and expansiblein its pertaining unsintered insulation material.

References Cited in the file of this patent UNITED STATES PATENTS

